The present invention relates to a circuit configuration, particularly, a circuit configuration implementing an NFC function in an environment where there is no power supply or using a power supply is restricted.
Equipping mobile phones (mobiles) with a Near Field Communication (NFC) function is now evolved, especially in Japan. In other countries, mobiles equipped with NFC are appearing on the market. Three modes are available in NFC: card mode, battery-less mode, and R/W (reader/writer) mode.
The R/W mode is a mode in which a mobile with NFC operates as a reader/writer and communicates with a PICC (IC card) existing in its surroundings. The card mode and battery-less mode are modes in which the mobile operates as a PICC and communicates with a reader/writer existing in its surroundings. A difference between the card mode and the battery-less mode is as follows: stable power is supplied externally in the card mode, whereas there is no such power in the battery-less mode.
Although three modes are available in NFC as mentioned above, a generally practiced development at the time of this application is such that a basic circuit design is typically made in the R/W mode and, on top of this basis, the remaining two modes are added. Therefore, in most cases, an ASK signal receiving circuit that is used in the R/W mode is also used in the card mode or battery-less mode.
NFC operations in the card mode, R/W mode, and battery-less mode (low consumption current mode) are well-known to those skilled in art, as exemplified by the following documents:
NXP NFC Controller PN544 for Mobile Phones and Portable Equipment, NXP Semiconductors http://www.nxp.com/documents/leaflet/75016890.pdf, retrieved 7 Nov. 2011.
ST21NFCA Near Field Communication Microcontroller, STMicroelectronics http://www.st.com/internet/mcu/product/207640.jsp, retrieved 7 Nov. 2011.